i used to use it at school sometime to make simple 3d renderings of site plans etc.
its not very hard, but the more complex stuff your trying to build that harder it gets to use. the snapping in it is fahken terrible.
when your first download it just screw around buy making boxs, spheres, pyramids, stack them on eachother, resize them etc. then start trying to build your ramp.
if you just go straight into trying to build your ramp you will end up chucking your computer out the window.